export default array => {
  const hash = {};

  // Loop though the array adding all the elements together in a hash
  array.forEach( num => {
    hash[ num ] = hash[ num ] + 1 || 1;
  } );

  // Loop through all the keys in the hash, returning the number if we have an
  // even number of occurances
  for ( const i in hash ) {
    if ( !( hash[ i ] & 1 ) ) {
      return Number( i );
    }
  }

  return false;
};
